Conventional portable drug delivery systems are driven typically by a lead screw mechanism that displaces a plunger of a drug reservoir to deliver the medication. The drug reservoir is embedded usually in a compartment, in which the plunger of the drug reservoir has to be physically connected to the lead screw or to the nut due to the siphoning effect. This effect can result in an unintended drug delivery when the pulling force of the fluid column in a catheter is higher than the friction force of the plunger.
In drug deliver systems which reuse the lead screw (and the nut), the drug reservoirs are mostly inserted from the top side of the device. Once the drug reservoir is inserted into the device and the plunger is connected to the lead screw, the drug reservoir has to be secured by a lid or by an adapter. In these devices, to insert a new reservoir that is full of fluid, it is necessary to reverse the direction of the lead screw until the piston engagement returns back to the starting position. Thus the drive system must be able to be reversed in direction. On the other hand, in solenoid or non-motor driven systems, the piston engagement must be reset manually when placing a newly filled or partially filled reservoir. Both types of reset methods are problematic in different manners.
For example, in motor rewind configurations, the motor must be capable of being reversed requiring additional switches and have complex circuitry. In addition, piston sensing is required to shut off motor at a home position, which consumes extra battery energy, and it is not possible to accommodate a partially filled cartridge without manually adjusting the drive system. Similarly, manual reset configurations also have inherent problems.
Typically, manual reset configurations require a more complex housing and a sophisticated nut mechanism to manually engage and disengage the threads. In addition, the disengagement mechanism is both difficult and costly to design and manufacture, the mechanism must be safeguarded from any inadvertent actuation, additional wear issues must be considered, and manual dexterity is required to perform proper function.